One manual system for guiding operators of vehicles to a designated location or along a path, such as directing an aircraft pilot to a specific airport terminal parking position, requires that the pilot follow manual signals given by a ground crewman. Various optical guidance systems not involving crewman also have been utilized. One optical system for guiding an aircraft to a gate utilizes the principle of parallax and projects different colored light rays from two units at separate locations. One unit is located behind a desired parking location while the second unit is located to one side of the parking area. Each unit has two neon lights therein. With regard to a straight-in approach, a red neon tube is located in a front portion and a green neon light is located in a back portion of one unit. Thus, if a pilot were positioned to the left of the guide-in position, he would see green to the left and red to the right in each unit which would indicate he should move to the right. The pilot would continue to move towards the one unit and to adjust his position laterally until he saw only a red light from the one unit. When the plane was at the desired parking position, he also would see only red light projecting from the side unit.
Another optical system for guiding aircraft to a gate utilizes pickup coils embedded in the gate apron to detect the position of the aircraft as it approaches a desired parking position at the terminal gate. Lights activated by the pickup coils provide guidance to the pilot. Problems of this system include the necessity of cutting into the apron to install the pickup coils which is undesirable and expensive. Moreover, constant freezing and heating of the apron causes breakage of wires which extend from the coils to a processing device which operates the lights.
Yet another optical system for guiding an aircraft to a gate utilizes a moire pattern generated by slatted grids. Typically two such grids are located at spaced locations. A pattern is generated by the angle of the first slatted grid to produce an arrow pointing in the lateral direction that the pilot needs to move to become aligned with the parking position. The second grid indicates the longitudinal distance from the position. A disadvantage of this system is that the pilot must look back and forth to each grid.
Still another optical guidance system for guiding an aircraft to a gate utilizes an interference pattern generated by a very strong light source behind an optical slit focused on the back of a lenticular lens which produces a dark line thereon by refraction. A pair of these lens are utilized in each system. The dark line formed on one of the lens moves left or right indicating the lateral position of the aircraft with respect to the parking area. On the remaining lens, the dark line moves from the bottom to the top of the lens to indicate the longitudinal distance of the craft from the parking location.
In each of the above discussed optical systems, two separate and independent visual indicators are utilized and both must be observed by an operator.
It has been found desirable to provide an optical guidance system utilizing a visual indicator at one location for directing vehicles to a predetermined location or along a predefined path.
Also, it has been found desirable to provide a unitary optical guidance apparatus having directional indicia to indicate lateral position of a vehicle with respect to a predetermined position as well as approach distance of the vehicle from said position.